Automatic back feed deburring is known in the art, as in the case of holes drilled through planer surfaces normal to the axis of the drill. In some cases a deburring tool, which may be of a hardened insert type, is spring loaded to automatically retract within the shank of the tool upon insertion through the hole; or in other cases the deburring tool may be actuated through a draw bar or similar mechanism to retract for entry and extend for back feed deburring, normally with a positive feed to a point where deburring at least is completed, and in some cases with a slight chamfer, at which time the tool is withdrawn.
A problem has persisted in holes drilled through workpieces having a forged or otherwise irregular non-planar inner surfaces so that a burr develops from drilling which may vary and project outside of a single plane normal to the axis of the drill. The removal of such burr may be more difficult when it occurs on an enclosed surface such as a hole drilled through a forged yoke involving a through hole with two inside hole edges requiring deburring. State of the art current practice involves manual "snagging" type deburring methods which can accommodate the irregular and inside location of non-planar burr edges which are involved.